Growth of large tetrapod-like ZnO crystals: I. Experimental considerations on kinetics of growth

A new method to grow large and uniform tetrapod-like crystals has been developed and the kinetics of the growth has been analyzed based on the reaction curves obtained experimentally. The formation of such crystals, having a leg length of 30 to 200 μm and an edge size of centering nucleus of 1 to 10 μm, is achieved by using ZnO/Zn particles prepared by oxidation of the surface of Zn powder, by making use of a smouldering reaction controlling the reaction rate, and by introducing zeolite as a reaction catalyst. The plot of the amount of O 2 absorbed during the reaction showed that the oxidation process proceeded parabolically and the reaction could be divided into two elementary reactions: the growth reaction of the nucleus and that of the succeeding legs, which can be controlled independently by the amount of zeolite added or the air-flow rate. The condition for reducing the secondary growth crystals like platelets between legs was elucidated by connecting the amounts of Zn reacted with the reaction rates.